Neuronal apoptosis resulting from high doses of the isoflavone genistein: role for calcium and p42/44 mitogen-activated protein kinase

• Published in: The Journal of pharmacology and experimental therapeutics Vol. 299; no. 1; p. 67
• Main Authors: Linford, N J, Yang, Y, Cook, D G, Dorsa, D M
• Format: Journal Article
• Language: English
• Published: United States 01-10-2001
• Subjects: Animals; Anticarcinogenic Agents - pharmacology; Apoptosis - physiology; Blotting, Western; Calcium - physiology; Caspases - metabolism; Cerebral Cortex - cytology; DNA Fragmentation - drug effects; Genes, bcl-2 - genetics; Genistein - pharmacology; In Vitro Techniques; Indicators and Reagents; L-Lactate Dehydrogenase - metabolism; Microscopy, Phase-Contrast; Mitogen-Activated Protein Kinase 1 - physiology; Neurons - physiology; Rats; Rats, Sprague-Dawley; Receptors, Estrogen - metabolism
• ISSN: 0022-3565

Genistein is a potent plant-derived isoflavone displaying estrogenic activity at low (nanomolar) concentrations and antiproliferative and antiangiogenic properties at higher concentrations (above 10-50 microM). The antiproliferative potential of genistein has made it an interesting candidate for cancer chemotherapy at high concentrations; however, the potential for genistein toxicity in neurons at such concentrations has not been previously addressed. We show that genistein is toxic to rat primary cortical neurons at a concentration of 50 microM, whereas daidzein, a structural analog, shows no toxicity at similar concentrations. The dying cells display an apoptotic morphology that is characterized by fragmented nuclei, appearance of apoptotic bodies, DNA laddering, and caspase-dependent poly(ADP-ribose) polymerase cleavage. This cell death is partially dependent on caspase activity, independent of estrogen receptors, and does not result in a significant loss of Bcl-2 or Bcl-X(L) protein. Genistein exposure induces delayed and prolonged activation of p42/44 mitogen-activated protein kinase (MAPK) and p38 MAPK but not c-Jun NH2-terminal kinase. The specific p42/44 MAPK kinase inhibitor PD98059 (50 microM) partially blocks genistein-induced apoptosis, whereas the p38 MAPK inhibitor SB202190 (10 microM) has no effect. Genistein elevates intracellular calcium and both 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-acetoxymethyl ester (1 microM) and dantrolene (10 microM) inhibit genistein-induced apoptosis, suggesting a link between genistein-induced intracellular calcium release and apoptosis. The combination of dantrolene and PD98059 block genistein-induced apoptosis in an additive manner compared with either compound alone. These findings provide evidence for a proapoptotic function of p42/44 MAPK and raise caution about potential side effects in the nervous system with genistein use as a high-dose therapeutic agent.